Aqueous emulsions of silicone resins are used in a variety of surface treatments such as additives in water based paints and coatings, as well as in treating textile materials. Silicone resins provide protection against wear and weather, increase water resistance or repellence, improve soil resistance, and allow water vapor permeation.
U.S. Pat. No. 4,582,874 discloses an aqueous emulsion of a low molecular weight silicone resin comprising by weight (a) 1-60% of a silicone resin (b) 0.1-10% of an emulsifier, and (c) water.
U.S. Pat. No. 5,443,627 teaches organopolysiloxane-alkyltrialkoxysilane emulsions for impregnating structural fiber-reinforced cement containing: components (A) organopolysiloxane free from basic nitrogen, (B) an alkyltrialkoxysilane, (C) an emulsifier and (D) water.
U.S. Pat. No. 5,531,812 discloses waterproofing agents for mineral building materials based on aqueous emulsions of organo-silanes and/or organosiloxane resins containing reactive groups in which the dispersed phase has an average particle size of 0.55 to 1.1 μm and a scope of particle size range of less than 1.3.
U.S. Pat. No. 6,262,171 discloses an aqueous emulsion comprising the components (A) organosilicone compositions selected from (A1) C1-C20-alkyl-C2-C6-alkoxysilanes and (A2) organopolysiloxane containing alkoxy groups, (B) organopolysiloxane containing, one or more siloxane units having SiC-bonded radicals containing basic nitrogen, with the proviso that the amine number of the organopolysiloxane is at least 0.01, and (C) an emulsifier. The said emulsions are used for making porous mineral building materials hydrophobic.
U.S. Pat. No. 6,294,608 discloses aqueous emulsions for imparting water repellency to building materials and wood. The '608 emulsions contain the components (A) organosilicon compounds which are selected from (A1) C1-C20-hydrocarbon-C1-C6-alkoxysilanes and (A2) branched organopolysiloxanes containing C1-C6-alkoxy groups, (B) organosilicon compounds which are selected from (B1) C1-C6-alkoxysilanes containing aminoalkyl groups and (B2) branched organosiloxanes containing aminoalkyl groups and (C) an emulsifier. The aqueous emulsions are suitable for imparting water repellency to porous mineral building materials and building coatings and to wood.
U.S. Pat. No. 4,877,654 relates to an aqueous silane emulsion comprising of a silane which is hydrolytically stable within a certain pH range, an emulsifier and a buffering compound providing the certain pH range.
The benefits resulting from using a silicone resin emulsion may be more pronounced if the silicone resin emulsion dries to a coherent resin film having good cohesion within the film and good adhesion to the substrate. Such coherent films may result from a silicone resin emulsion in which the emulsion droplets contain groups or functionality that react with each other and with the substrate upon water removal. This later process is sometimes referred to as “post curing”, as opposed to “pre-curing” where the oil phase within the emulsion droplets is crosslinked prior to application and thus becomes non-reactive. However, silicone resin emulsions where the silicone resin contains a substantial quantity of reactive groups, especially hydrolytically reactive groups, poses several challenges. For example, silicone resin emulsions have poor shelf stability due to resin hydrolysis, which often produces an alcohol that destabilizes the emulsion. Another mechanism is resin condensation which results in emulsion breaking or gelling. Even when emulsion remains stable, the silicone resin in the emulsion droplet may slowly react such that with time, it loses some or all of the reactive groups and as a result, the film formed from an aged emulsion has much diminished strength and adhesion or binding ability as compared to that of a freshly prepared emulsion.
Another problem encountered with emulsions containing reactive silicone resins is that the “post curing” does not reach completion after water removal, leaving either a liquid layer on substrate or a film which is tacky or greasy. This problem may be circumvented if the substrate material is such that it promotes post curing in the adhering film, but this will largely limit the choice of the substrate. Alternatively, a catalyst can be incorporated in the emulsion. However the use of a catalyst in the emulsion has the disadvantage that the emulsion needs to be used immediately after preparation, otherwise the oil phase tends to pre-maturely react thus becomes hardened such that the film resulted from an aged emulsion loses its mechanical strength. Thus, there is a need to identify emulsions of silicone resins that have good storage stability and provide solid, non-tacky coatings upon drying on any surface application, and are free of catalysts.